In the course of erecting steel structures, a thick coating of inorganic material is commonly applied to the metallic structural elements to achieve a number of objectives including fire retardation, improved appearance and sound deadening. While several types of formulations have been applied for these purposes over the years by means of a variety of techniques, the most successful system so far consists in spraying onto the steel surfaces settable aqueous mixes composed essentially of calcined gypsum, a lightweight inorganic aggregate material such as exfoliated vermiculite or shredded expanded polystyrene to lower the density of the mix, a mixture of fibrous materials such as a high wet bulking cellulose fiber and glass fiber, and an air entraining agent to render the wet mixture pumpable. A composition of this type is described by Bragg in U.S. Pat. Nos. 3,719,573 and 3,839,059, along with the most desirable application technique, i. e., pumping the aqueous mix and spraying it directly onto the steel in one layer. Such slurries are generally prepared at ground level and are pumped to the point of application, where they are spray-applied to the substrate. Often the point of application exceeds 20 or 30 stories where high rise construction is involved. Accordingly, pumpability of the slurries is an important criterion in their formulation and preparation. The slurries must be able to hold the large quantity of water that renders them capable of being pumped easily and to great heights, yet they must retain a consistency sufficient to prevent segregation or settling of ingredients and permit adequate yield or coverage of the substrate at a given thickness. The coating mixes must also adhere to the substrate, both in the slurried state during application, and in the dried or xe2x80x9csetxe2x80x9d state after application. In addition, the mix must set without undue expansion or shrinkage that could result in the formation of cracks that would seriously deter from the insulative value of the dry coating.
In the conventional process, fireproofing mixes are transported to the application site as dry mixtures and in a mixer an appropriate amount of water is added to form the pumpable slurry. The slurry is pumped from temporary holding equipment to the point of application. Where the components are pumped over distances, premature set-up can occur prior to reaching the final destination. In addition, the preparation and application processes may span many hours. Accordingly, the setting time of the mix is generally retarded by the inclusion of set retarding agents to provide an acceptable field pot life. In addition, air-entraining agents such as alpha-olefin sulfonate and sodium lauryl sulfate are used to aid pumpability of the slurry.
U.S. Pat. No. 4,904,503 to Hilton et al. teaches that acceleration of the setting time and also the xe2x80x9cyieldxe2x80x9d of the aforedescribed pumped and sprayed fireproofing mixes is obtained by injecting an acidic set accelerating agent such as alum into the slurry prior to spraying. The acid agent, prior to causing accelerated set, reacts with basic material such as calcium carbonate present in the mix to generate gas such as carbon dioxide. The evolved gas expands or foams the slurry which further reduces the density and increases the volume of the applied fireproofing after setting per given weight of dry fireproofing used. Such xe2x80x9cchemically foamedxe2x80x9d, xe2x80x9chigh yieldxe2x80x9d spray fireproofing has been successfully commercialized around the world.
The xe2x80x9cyieldxe2x80x9d or volume of applied fireproofing per weight of dry mix is an important factor in the commercial success of the product. The higher the yield, the more coverage an applicator can obtain for a given amount of formulation. Yield is generally calculated by methods known in the art as board feet per dry weight of composition.
U.S. Pat. No. 3,963,507 discloses a foaming mortar containing specific ratios of water-soluble, low-viscosity cellulose derivatives such as methyl cellulose, ethyl methyl cellulose and hydroxyethyl methyl cellulose; high-viscosity cellulose derivatives, and polyvinyl alcohol as a foaming accelerator.
U.S. Pat. No. 4,518,652 discloses a method for producing gypsum wallboard by producing a foam comprising polyvinyl alcohol and water, introducing the foam into an aqueous cementitious slurry, depositing the slurry between paper cover sheets, and allowing the slurry to set. An emulsion of asphalt and wax can be added to the cementitious slurry to impart water resistance.
U.S. Pat. No. 4,518,652 forms lightweight gypsum wallboard by incorporating pre-generated foams into gypsum slurries followed by setting of the foam-slurry mix. The foam is formed by dissolving polyvinyl alcohol in water and placing it into a high shear foaming apparatus.
It would be desirable to produce a pumpable, low density, high yielding sprayable fireproofing composition that eliminates or reduces the need for a lightweight aggregate.
It further would be desirable to produce a low density, high yielding, pumpable, sprayable fireproofing composition that can be easily prepared at the site of the application without the need for high shear foaming devices and the like, and which upon application, results in excellent yields.
The present invention relates to a formulation adapted to form a foamed cementitious composition, the foamed cementitious composition itself, a method of forming a hydraulic binder foam, and a method of conveying and applying the resulting foam to a substrate. More specifically, a pumpable cementitious slurry is formed, the slurry is mixed with a gas such as air, and is subjected to mechanically created turbulence to generate gas bubbles and create a foam, which preferably is stabilized by a foam stabilizing agent such as polyvinyl alcohol present in the slurry. The foam is then conveyed to a nozzle or other suitable dispense point from which it is applied, for example sprayed, preferably uniformly, onto a substrate to be coated. Prior to dispensing, a set accelerator is preferably injected, which causes the foam to gel, which in turn improves the hangability of the product on a substrate. The spray material adheres to the substrate and hardens to form an insulative coating on the substrate. The particularly preferred compositions are capable of providing a high yield of fireproofing that can be applied to substrates at typical commercial application rates of about 1800 boardfeet/hour.
The present invention is also directed to a dry composition comprising a hydratable cementitious binder, a mechanical foam stabilizing agent, and optionally a fibrous component, set retarder and air entraining agent, said composition providing, on the addition of water, gas and mechanical turbulence, a settable foam which is capable of spray application to a steel structural member and which, after spray application, is adherent to the member in the foamed state and after setting. The foam after setting, forms a fire and heat protective adherent coating on the member.